Protection circuit for battery management system

ABSTRACT

Systems and methods are provided for a battery management system (BMS) having a protection circuit. In one example, a vehicle battery system may include the BMS, the BMS including a cutoff circuit coupled to a short-circuit protection circuit, and a battery pack, wherein the short-circuit protection circuit may include a diode array, cathodes of the diode array being coupled to a positive terminal post of the battery pack and anodes of the diode array being coupled to a negative terminal post of the battery pack. In some examples, the cutoff circuit may further be coupled to a reverse bias protection circuit including a switchable current path arranged between a control input of the cutoff circuit and an output of the cutoff circuit. In this way, the vehicle battery system may be protected from unexpected voltage conditions via the BMS redirecting and dissipating excess current away from the cutoff circuit.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. Non-ProvisionalApplication No. 17/342,447, entitled “PROTECTION CIRCUIT FOR BATTERYMANAGEMENT SYSTEM” and filed on Jun. 8, 2021. U.S. Non-Provisionalapplication Ser. No. 17/342,447 claims priority to U.S. ProvisionalApplication No. 63/036,346, entitled “PROTECTION CIRCUIT FOR BATTERYMANAGEMENT SYSTEM” and filed on Jun. 8, 2020. U.S. Non-Provisionalapplication Ser. No. 17/342,447 claims further priority to U.S.Provisional Application No. 63/042,963, entitled “PROTECTION CIRCUIT FORBATTERY MANAGEMENT SYSTEM” and filed on Jun. 23, 2020. The entirecontents of each of the above-identified application are herebyincorporated by reference for all purposes.

FIELD

The present description relates generally to a battery management systemincluding a protection circuit, in particular for a battery pack in avehicle.

BACKGROUND AND SUMMARY

Lithium-ion secondary (rechargeable) batteries are commonly employed forstarting and powering electric and hybrid-electric vehicles. Accordingto power requirements and application, a plurality of lithium-ionbatteries may be assembled into a battery pack. For example, a 48 Vbattery pack may be installed in a battery-assisted hybrid vehicle(BAHV) so as to provide power to the BAHV during operations having lowengine load, such as coasting, braking, and idling.

Under certain conditions, such as during a short-circuit event,relatively high currents (for example, up to 1700 A) may be generatedacross the battery pack or across a battery management system (BMS)electrically coupled thereto. Such high currents may result in voltagespikes which risk degradation to electronic components included in theBMS, such as metal-oxide-semiconductor field-effect transistors(MOSFETs) and/or other switches and relays.

Accordingly, protection circuits have been developed to mitigate suchvoltage spikes. As one example, a current detection circuit may beimplemented in the BMS to detect a higher current characteristic of ashort-circuit event, permitting the BMS to timely switch OFF a givenMOSFET at risk of receiving the higher current. However, even if thehigher current is detected in time to successfully switch OFF the MOSFETin the BMS, energy accumulated in inductive elements, such as in anelectrical load, or in electrical lines coupling battery systemcomponents may result in the MOSFET being conducted (that is, reaching abreakdown voltage) and entering avalanche mode. The MOSFET may thereforebe at risk of degradation even when switched OFF.

The inventors have identified the above issues and have determinedsolutions to at least partially solve them. In one example, a vehiclebattery system is provided, the vehicle battery system including abattery management system (BMS) including a cutoff circuit electricallycoupled to a short-circuit protection circuit, and a battery pack, wherea positive supply line of the battery pack is electrically coupled tothe cutoff circuit and where a ground return line of the battery pack iselectrically coupled to the short-circuit protection circuit, whereinthe short-circuit protection circuit includes a diode array, wherecathodes of the diode array are directly electrically coupled to apositive terminal post of the battery pack and anodes of the diode arrayare directly electrically coupled to a negative terminal post of thebattery pack. In this way, the vehicle battery system may be protectedfrom degradation by redirecting and dissipating current resulting fromundesirable voltage conditions.

In one example, a vehicle battery system is provided having a batterypack coupled to a BMS. Specifically, a positive supply line of thebattery pack may be electrically coupled to a drain terminal of a MOSFETincluded in the BMS and a ground return line of the battery pack may beelectrically coupled to a diode array. Further, a gate terminal and asource terminal of the MOSFET may be electrically coupled to a reversebias protection circuit, the source terminal further electricallycoupled to the diode array. Accordingly, in a higher-current environmentaccompanying application of a reverse bias voltage or a short-circuitevent, a gate-source voltage (V_(GS)) of the MOSFET may be maintainedbelow a threshold voltage (V_(th)) by directing current to a low-currentleakage transistor in the reverse bias protection circuit. As such, thereverse bias protection circuit may maintain an OFF state in the MOSFETeven upon application of the reverse bias voltage or during theshort-circuit event.

The diode array may provide an additional low-resistance path forcurrent dissipation when the MOSFET is switched OFF due to reverse biasvoltage or short-circuit conditions. Specifically, the diode array maybe coupled between positive and negative terminal posts of the batterypack such that current may cycle across an electrical load and the diodearray and thereby dissipate energy accumulated in the vehicle batterysystem. As such, the reverse bias protection circuit and the diode arraymay function in tandem to redirect and dissipate excess currentgenerated in the vehicle battery system, thereby preventing the MOSFETboth from switching ON and from surpassing a breakdown voltage whenswitched OFF.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a schematic diagram of an exemplary battery pack assembly.

FIG. 1B shows a schematic diagram of the exemplary battery pack assemblywith at least a portion of an external housing removed, exposing aplurality of stacked battery cells.

FIG. 2 shows a high-level block diagram of a vehicle battery systemincluding a battery management system.

FIG. 3A shows a schematic diagram of circuitry of a reverse biasprotection circuit included in the battery management system.

FIG. 3B shows a schematic diagram of circuitry of a short-circuitprotection circuit.

FIG. 4 shows a flow chart of a method for managing current flow during areverse bias voltage condition.

FIG. 5A shows first and second example operating sequences for the BMS.

FIG. 5B shows a third example operating sequence for the BMS.

FIG. 6 shows a schematic diagram of an exemplary printed circuit boardassembly for implementing the battery management system.

DETAILED DESCRIPTION

The following description relates to systems and methods for aprotection circuit for a battery pack, for example, a lithium-ionbattery pack for powering an electric or hybrid-electric vehicle. Thelithium-ion battery pack may include a plurality of lithium-ion batterycells assembled in a stacked configuration. As an example, thelithium-ion battery pack may be a 48V battery pack for starting orproviding power to a battery-assisted hybrid vehicle (BAHV). Further,the protection circuit may be included in a battery management system(BMS) coupled to the lithium-ion battery pack.

Specifically, the protection circuit may maintain a cutoff circuit in anOFF state upon application of an unexpected reverse bias voltage, forexample, due to a reversed polarity event. The cutoff circuit mayinclude one or more of field-effect transistors (FETs), such asmetal-oxide semiconductor FETs (MOSFETs), junction gate FETs (JFETs),etc., other types of transistors, or a combination thereof. In oneexample, the cutoff circuit may be a single MOSFET. In an additional oralternative example, the protection circuit may include a low-currentleakage transistor, such as a bipolar junction transistor (BJT), whichmay maintain a gate-source voltage (V_(GS)) of the MOSFET below athreshold voltage (V_(th)) by maintaining a near-zero collector-emittervoltage (V_(CE)) when the reverse bias voltage is applied to a sourceterminal of the MOSFET.

The protection circuit may further protect the cutoff circuit fromreaching a breakdown voltage and conducting upon being switched OFF, forexample, when a voltage spike is detected by the BMS during ashort-circuit event. Specifically, the protection circuit may include adiode array coupled to the source terminal of the MOSFET, where cathodesand anodes of the diode array may further be coupled to an electricalload coupled to each of the battery pack and the BMS. In one example,the diode array may include a plurality of flyback or freewheelingdiodes. Accordingly, energy accumulated before or during the voltagespike may be cycled and dissipated across the diode array and theelectrical load. In this way, the cutoff circuit, and thereby the BMSand the lithium-ion battery pack, may be protected from voltage spikesincurred by both reversed polarity situations, such as due to negativeelectric noise or positive and negative leads miscoupled to terminalposts of the lithium-ion battery pack, and short-circuit situationswhich may otherwise send the MOSFET into avalanche mode. Further, theprotection circuit provided by the present disclosure may protect theBMS from relatively high currents (for example, up to 1700 A), even atrelatively high temperatures (for example, up to 140° C.), and mayextend acceptable lifetime degradation, such that the BMS may continueto function within an expected longevity of individual hardwarecomponents included therein.

As used herein, when referring to two components of a circuit, “coupled”may refer to “electrically coupled” unless otherwise specified.Accordingly, when referring to two components of a circuit, “directlycoupled” may refer to the two components being electrically coupledwithout any electrical components (e.g., resistors, transistors,capacitors, etc.) disposed therebetween, excepting an electricalconductor (such as a wire and/or a busbar). In addition, transistorsdescribed as being “ON” allow current to flow through the transistors,whereas transistors described as being “OFF” prevent or substantiallyrestrict current flow through the transistors (“substantially” may beused herein as a qualifier meaning “effectively”).

FIG. 1A depicts an exemplary battery pack assembly for a vehicle system.FIG. 1B depicts the battery pack assembly with at least a portion of anexternal housing thereof removed, such that a battery pack including aplurality of stacked lithium-ion battery cells is exposed. The batterypack may be included in the exemplary vehicle battery system of FIG. 2 ,where the battery pack may be coupled to a BMS. The BMS may include aprotection circuit, exemplary circuitry of which is depicted in FIGS. 3Aand 3B. In some examples, the protection circuit may be configured tomaintain a cutoff circuit of the BMS in an OFF state when no switch ONrequest has been received. In additional or alternative examples, theprotection circuit may be configured to maintain at least one componentof the cutoff circuit in the OFF state even when a switch ON request isreceived, so that electric current flow from one or more of theplurality of stacked lithium-ion battery cells to an electrical load maybe prevented. However, in such examples, it will be appreciated thataccumulated energy in the vehicle battery system may be cycled throughthe electrical load. Accordingly, a method for managing current flowthrough the cutoff circuit, for example, which may include maintainingthe cutoff circuit in the OFF state and dissipating any accumulatedenergy, is provided in FIG. 4 . Example operating sequences of the BMSfor managing current flow through the cutoff circuit and the protectioncircuit are provided in FIGS. 5A and 5B. FIG. 6 provides one exemplaryprinted circuit board assembly (PCBA) for implementing the BMS includingthe protection circuit, where the PCBA may include a plurality ofbusbars for coupling various components in the vehicle battery systemand mitigating parasitic inductances.

Referring now to FIG. 1A, a schematic diagram 100 depicting a batterypack assembly 102 is shown. The battery pack assembly 102 may beconfigured for starting or powering a vehicle, such as an electricvehicle or a hybrid-electric vehicle. For example, the battery packassembly 102 may include a 48V battery pack including a plurality oflithium-ion battery cells (as described below in detail with referenceto FIG. 1B).

The plurality of lithium-ion battery cells may be arranged in a stackedconfiguration and removably enclosed within an external housing 104.Accordingly, the external housing 104 may be composed of a materialhaving a low electrical conductivity, such as a plastic or otherpolymer, so as to reduce shorting events within the vehicle. Theexternal housing 104, depicted in FIG. 1A as a rectangular prism, may bemolded to be clearance fit into the vehicle such that the battery packassembly 102 may be in face-sharing contact with one or more componentsof the vehicle, such as one or more engine components.

The external housing 104 may further be configured to include openingsor cavities for interfacial components of the battery pack assembly 102.For example, the external housing 104 may be configured to expose apositive terminal post 106 and a negative terminal post 108, which mayeach be a lead-free terminal, for example. That is, the positiveterminal post 106 and the negative terminal post 108 may beinsert-molded in place on the external housing 104. Within the vehicle,the positive terminal post 106 and the negative terminal post 108 mayrespectively be electrically coupled to positive and negative leads suchthat the battery pack assembly 102 may form a closed circuit with anelectrical load of the vehicle, such that power may be provided to thevehicle.

The positive terminal post 106 and the negative terminal post 108 may beconfigured with differing colors, shapes, symbols, etc. so as toindicate which of the terminal posts 106, 108 is positive and which isnegative. For example, the positive terminal post 106 may be red anddenoted with a plus symbol (+) and the negative terminal post 108 may beblack and denoted with a negative symbol (−). Nevertheless, in somecircumstances the positive and negative leads may be erroneouslymiscoupled, such that the positive lead may be coupled to the negativeterminal post 108 and the negative lead may be coupled to the positiveterminal post 106. In such circumstances, a reversed bias of appliedpotential difference may result, and the battery pack assembly 102 mayunexpectedly discharge absent any protection thereagainst. Accordingly,and as discussed below with reference to FIGS. 2 and 3A, the batterypack assembly 102 may include a BMS having a reverse bias protectioncircuit, where the BMS may be coupled to the plurality of lithium-ionbattery cells and the electrical load. In this way, a MOSFET of the BMSmay remain switched OFF during application of a reverse bias voltagesuch that degradation of individual battery cells and the BMS may bemitigated.

In some examples, the external housing 104 may be configured to expose anetwork management interface 110. In one example, the network managementinterface 110 may be communicatively coupled to a local interconnectnetwork (LIN) 112 of the vehicle via a wired or wireless connection.Accordingly, in some examples, the network management interface 110 mayinclude a physical connector for mating with a complementary connectoraffixed to a wire extending from a LIN bus.

In some examples, the external housing 104 may include a top cover 114 aremovably affixed to an enclosure base 114 b. As such, the top cover 114a may be temporarily removed to replace or diagnose one or more of theplurality of lithium-ion battery cells.

Referring now to FIG. 1B, a schematic diagram 150 depicting a batterypack 152 is shown. In some examples, the battery pack 152 may beincluded in the battery pack assembly 102 of FIG. 1A, wherein the topcover 114 a has been removed from the battery pack assembly 102,exposing a plurality of lithium-ion battery cells 154 removably affixedto the enclosure base 114 b. Accordingly, it will be appreciated thateach lithium-ion battery cell 154 may represent a fundamental unit fromwhich a battery pack of arbitrary size, arbitrary power, and having anarbitrary number of lithium-ion battery cells 154 may be constructed. Itwill further be appreciated that other embodiments not depicted at FIG.1B may include a battery pack having only one lithium-ion battery cell.

In some examples, the plurality of lithium-ion battery cells 154 may bearranged in a stacked configuration, where each of the plurality oflithium-ion battery cells 154 may be a prismatic pouch electrochemicalcell. As such, each of the plurality of lithium-ion battery cells 154may include a positive electrode and a negative electrode immersed in aliquid electrolyte, where each of the positive electrode, negativeelectrode, and electrolyte may be enclosed by a hermetically-sealedpouch.

Further, each of the plurality of lithium-ion battery cells 154 mayexpose a positive electrode tab 156 and a negative electrode tab 158,which may be configured to couple to the positive electrode and thenegative electrode, respectively. Accordingly, each of the plurality oflithium-ion battery cells 154 may be electrically coupled to thepositive terminal post 106 and the negative terminal post 108 describedin detail above with reference to FIG. 1A. In some examples, theplurality of lithium-ion battery cells 154 may be electrically coupledto one another in series and/or in parallel by one or more busbars (notshown at FIG. 1B), whereby the one or more busbars may each beelectrically coupled to a plurality of electrode tabs 156, 158 onmultiple lithium-ion battery cells 154. The one or more busbars mayfurther be electrically coupled to one of the terminal posts 106, 108,such that the plurality of lithium-ion battery cells 154 may beelectrically coupled to the terminal posts 106, 108 and thereby providepower to a system, for example, a vehicle.

Each lithium-ion battery cell 154 of the battery pack 152 may beidentical to one another. Further, each of a total number of lithium-ionbattery cells 154 and an electrical coupling configuration (e.g.,parallel count and series count) of the battery pack 152 may defineelectrical characteristics and performance ratings thereof. As anexample, the battery pack 152 may be configured in a ‘4S4P’configuration which has 16 lithium-ion battery cells 154 in foursubgroups, where the subgroups may be electrically coupled in series,and where four lithium-ion battery cells 154 in each subgroup may beelectrically coupled in parallel. In some examples, the total number oflithium-ion battery cells 154 may be odd. In other examples, the totalnumber of lithium-ion battery cells 154 may be even.

The plurality of lithium-ion battery cells 154 may be retained in thestacked configuration by bands 160. As shown, one or more bands 160 maycircumscribe the plurality of lithium-ion battery cells 154 so as toprevent displacement of individual lithium-ion battery cells 154relative to one another.

Referring now to FIG. 2 , a high-level block diagram 200 depicting avehicle battery system 202 is shown. The vehicle battery system 202 mayinclude a battery pack 204 (such as the battery pack 152 of FIG. 1B),the battery pack 204 including one or more lithium-ion battery cells222. As shown, a positive supply line 252 may couple a positive end ofthe battery pack 204 to an electrical load 206 (for example, a beltintegrated starter/generator, an integrated starter/generator, etc.) viaa BMS 208, and a ground return line 254 may couple the electrical load206 to a negative end of the battery pack 204. Specifically, thepositive supply line 252 of the battery pack 204 may be coupled to aninput 256 a of a cutoff circuit 210, and an output 256 c of the cutoffcircuit 210 may be coupled to the electrical load 206. Further, acontrol input 256 b of the cutoff circuit 210 may be coupled to a driverintegrated circuit (IC) 212 of the BMS 208 via a protection circuit 214.Accordingly, the driver IC 212 may be communicably coupled to acontroller 272, which may store machine readable instructions on anon-transitory storage device, the instructions executable by thecontroller 272 to enable various functionalities of the BMS 208, such asreceiving and transmitting switching requests, monitoring the vehiclebattery system 202, etc. For example, a current detection circuit 232coupled to the positive supply line 252 via a node 270 may transmitmeasurements of currents passing to the cutoff circuit 210 to thecontroller 272, where the controller 272 may be enabled to generateswitching requests and adjust battery system operating conditions inresponse to the measurements received thereat. It will be appreciatedthat, though the controller 272 is depicted in FIG. 2 as being includedwithin the driver IC 212, in other examples, the controller 272 may bepositioned external to the driver IC 212.

As further shown, a positive terminal post 216 may be coupled to a linecoupling the BMS 208 to the electrical load 206 and a negative terminalpost 218 may be coupled to a line (the ground return line 254) couplingthe electrical load 206 to the battery pack 204 [additionally oralternatively, the positive and negative terminal posts 216, 218 may becoupled to the BMS 208 via respective busbars (not shown at FIG. 2 )].Accordingly, it will be appreciated that the electrical load 206 may belocated external to the battery pack 204. A diode array 234 may furtherbe coupled to each of the positive and negative terminal posts 216, 218,where anodes of each diode in the diode array 234 may be directlycoupled to the negative terminal post 218 and cathodes of each diode inthe diode array 234 may be directly coupled to the positive terminalpost 216. A shunt resistor 262 may further be positioned along theground return line 254 coupling the battery pack 204 to the negativeterminal post 218.

The cutoff circuit 210 may be coupled to other components in the vehiclebattery system 202 via the input 256 a, the control input 256 b, and theoutput 256 c. As such, a voltage at the control input 256 b relative toa voltage at the output 256 c may control an operating state of thecutoff circuit 210. For example, if a relative voltage across thecontrol input 256 b and the output 256 c is less than a thresholdoperating voltage, then the cutoff circuit 210 may be in an OFF state.Conversely, if the relative voltage across the control input 256 b andthe output 256 c is greater than or equal to a threshold operatingvoltage, then the cutoff circuit 210 may be in an ON state. In this way,the cutoff circuit 210 may operate as a switch to selectively permitcurrent flow from the input 256 a to the output 256 c depending on avoltage applied to the control input 256 b.

The cutoff circuit 210 may include one or more of FETs, such as MOSFETsor JFETs, other types of transistors, or combinations thereof. In someexamples, the cutoff circuit 210 may be a single MOSFET, such as ann-channel enhancement mode MOSFET, a p-channel enhancement mode MOSFET,etc. In such examples, the input 256 a may be a drain terminal, thecontrol input 256 b may be a gate terminal, and the output 256 c may bea source terminal. Accordingly, as an exemplary embodiment, operation ofthe cutoff circuit 210 may be described hereinbelow as operation of aMOSFET 210 having a drain terminal 256 a, a gate terminal 256 b, and asource terminal 256 c.

Specifically, the MOSFET 210 may be in an OFF state at zero gate-sourcevoltage (V_(GS)). Thus, switching the MOSFET 210 to an ON state maydepend upon a voltage at the gate terminal 256 b (V_(G)) relative to avoltage at the source terminal 256 c (V_(S)), that is, the V_(GS) If theV_(GS) is higher than a V_(th) of the MOSFET 210, then the MOSFET 210may switch from the OFF state to the ON state. When in the ON state, theMOSFET 210 may permit current flow from the drain terminal 256 a to thesource terminal 256 c. Conversely, when in the OFF state, the MOSFET 210may prevent or restrict (e.g., substantially restrict) current flowtherethrough.

During battery operation, a switch ON request may be received by thedriver IC 212, and the V_(GS) (greater than the V_(th)) may be output toswitch the MOSFET 210 to the ON state. However, in some circumstances,the MOSFET 210 may be unintentionally switched from an OFF state to anON state without any feedback from the driver IC 212. For example, ahigher-current or short-circuit voltage profile may be generated by areversed polarity event, by negative electric noise in the vehiclebattery system 202, etc.

Specifically, an unintentional switching of the MOSFET 210 may resultfrom any event which would generate a significant negative V_(S), as anegative V_(S) may result in a positive V_(GS), as implied by equation(1):

V _(GS) =V _(G) −V _(S)  (1)

As just one example, if the V_(G) is zero and the V_(S) is a negativevalue, then the V_(GS) is a positive value, and if the positive value ofthe V_(GS) is greater than the V_(th), then the MOSFET 210 may turn ON.

Accordingly, a protection circuit to maintain a MOSFET in an OFF stateduring an unexpected voltage spike in the vehicle battery system isprovided herein. For example, the protection circuit 214 may be includedin the BMS 208 to protect the MOSFET 210 from unintentional switch ON bydissipating energy accumulated in the vehicle battery system 202 duringa short-circuit or higher-current situation. Accordingly, the protectioncircuit 214 may control the gate terminal 256 b and the source terminal256 c of MOSFET 210 by maintaining the V_(G) and the V_(S) near, orsubstantially at, zero, such that a magnitude of the V_(GS) may bemaintained at a low value and may not exceed the V_(th).

For a circuit that does not include a reverse bias protection circuitdescribed herein, current at a charge pump included in the driver IC 212may bleed out to compensate leakage current at the MOSFET 210 duringreverse bias conditions. Accordingly, the vehicle battery system 202 maylose built-up charge at the charge pump, such that the driver IC 212 maynot be able to effectively supply current to various parts of thevehicle battery system 202 (for example, to switch ON the MOSFET 210when a switch ON request is actually received). Thus, when a suddennegative V_(S) is generated at the MOSFET 210, current draining from thecharge pump may be undesirably exacerbated.

In contrast, in the present disclosure, the protection circuit 214prevents the charge pump from bleeding out once negative V_(S) isdetected above a threshold V_(S). Specifically, and as discussed belowin detail with reference to FIG. 3A, a current path may be provided inthe protection circuit 214 via a pair of diodes in series to allowcurrent to flow to the gate terminal 256 b of the MOSFET 210.

To maintain the V_(GS) less than the V_(th), the protection circuit 214may further include a switchable current path arranged between the gateterminal 256 b and the source terminal 256 c. The switchable currentpath may include a transistor or switching device, such as a BJT, whichmay, responsive to detecting an unexpected negative V_(S), maintain downthe V_(GS) at the MOSFET 210 to maintain the MOSFET 210 in the OFFstate. Thus, by reducing current drain at the charge pump and preventingthe MOSFET 210 from turning ON absent any switch ON request, theprotection circuit 214 may mitigate degradation of the BMS 208 and theone or more lithium-ion battery cells 220 in the battery pack 204,thereby allowing the BMS 208 to continue expected functionality, such asprotecting the battery pack 204 from deep discharge.

In this way, the BMS 208 may be configured to flow current through theswitchable current path of the protection circuit 214 upon detection ofthe reverse bias voltage at the output 256 c of the cutoff circuit 210(e.g., at the source terminal 256 c of the MOSFET 210). The BMS 208 mayfurther be configured to prevent current flow through the switchablecurrent path in response to an absence of the reverse bias voltage atthe output 256 c of the cutoff circuit 210 (e.g., at the source terminal256 c of the MOSFET 210).

It will be appreciated that, though a single MOSFET 210 is depicted atFIG. 2 , the BMS 208 may include an array of MOSFETs. Accordingly,aspects of the present disclosure may be applied to each MOSFET in thearray of MOSFETs, such that each MOSFET in the array of MOSFETs may beprotected from unexpected switch ON.

The BMS 208 may further be enabled to switch OFF the MOSFET 210 from apreviously requested ON state. For example, during a short-circuitevent, a voltage spike (e.g., a change in magnitude of voltage thatexceeds a threshold voltage, a voltage greater than the voltage of thebattery pack, etc.) may result in the electrical load 206 beingpartially bypassed, generating excess current which may be passedtowards the MOSFET 210 along the positive supply line 252. Accordingly,to prevent the excess current from degrading the MOSFET 210, the currentdetection circuit 232 may be implemented to detect the excess current,enabling the driver IC 212 to execute a switch OFF request and open theMOSFET 210.

Accordingly, in one example, the current detection circuit 232 may beelectrically coupled to the positive supply line 252 at the node 270.However, it will be appreciated that in other examples, the currentdetection circuit 232 may be coupled to other lines or components of thevehicle battery system 202, such as the ground return line 254. Thecurrent detection circuit 232 may further be communicably coupled to thedriver IC 212 via the controller 272 included therein. The currentdetection circuit 232 may detect and obtain a measurement of a currentpassing through the node 270, whereby the measurement may be transmittedto the driver IC 212. Thereat, the controller 272 may generate theswitching request for the driver IC 212. In this way, the BMS mayprotect the MOSFET and other components of the vehicle battery systemfrom undesired currents that may result from short-circuit events.

In addition, it may be possible to reduce a possibility of a breakdownvoltage of the MOSFET 210 being reached even when the MOSFET 210 isswitched OFF. Specifically, less energy accumulated prior to, or during,a voltage spike may be passed to the MOSFET 210 so that the MOSFET 210may not enter avalanche mode, risking degradation of the MOSFET 210. Inthe BMS 208, the diode array 234 may provide a low-resistance path fordissipation of the accumulated energy.

Specifically, the diode array 234 may include a plurality of flyback orfreewheeling diodes, where anodes of each of the plurality offreewheeling diodes may be directly coupled to the negative terminalpost 218 and cathodes of each of the plurality of freewheeling diodesmay be directly coupled to the positive terminal post 216. When theMOSFET 210 is switched OFF in response to a short-circuit event, thepositive terminal post 216 may have a lower potential thereat, such thatthe negative terminal post 218 may have a higher potential than thepositive terminal post 216. Accordingly, when excess current accumulatedat the electrical load 206 passes along the ground return line 254 tothe negative terminal post 218, a potential difference generated betweenthe positive and negative terminal posts 216, 218 may draw the currentacross the diode array 234. Due to the potential difference generatedupon switching OFF of the MOSFET 210, it will be appreciated that thecurrent may begin flowing across the diode array 234 substantiallyimmediately following switching OFF of the MOSFET 210. Specifically, theplurality of freewheeling diodes may by characterized a fast forwardresponse time, resulting in the low-resistance path. As shown, the shuntresistor 262 may be implemented to further direct the current across thelow-resistance path provided by the diode array 234.

Since the MOSFET 210 may be maintained OFF by the protection circuit214, the current passed across the diode array 234 may further be passedacross the electrical load 206 to be received again at the negativeterminal post 218. In this way, excess current may cycle across each ofthe electrical load and the diode array. As the current cycles, energymay dissipate from the vehicle battery system 202 (for example, viaheat) until the (gradually attenuating inductive) current is reducedbelow a threshold current manageable by the MOSFET 210. Thereafter, thedriver IC 212 may be enabled to switch the MOSFET 210 ON again inresponse to a switch ON request being generated by the controller 272,an external controller, or an operator of the vehicle battery system202. However, it will be appreciated that the low-resistance pathprovided by the diode array 234 may permit current to cycle thereacrosswhenever the MOSFET 210 is switched OFF. That is, in some examples, thelow-resistance path may cycle and dissipate currents of up to 1700 Awhenever the MOSFET 210 is switched OFF. For example, the low-resistancepath may cycle and dissipate a current of 200-300 A when the vehiclebattery system 202 is powered down as expected and a current of greaterthan 1000 A during and following a short-circuit event. In this way, thediode array may redirect and dissipate accumulated energy when thevehicle battery system is powered down, whether the BMS switches OFF theMOSFET in response to an operator request or a short-circuit event.

Referring now to FIG. 3A, a schematic diagram 300 depicting circuitry ofone example of a reverse bias protection circuit 314 included in a BMS308 is shown. In some examples, one or more components described withreference to FIG. 3A may be substituted into the vehicle battery system202 described above with reference to FIG. 2 . For example, the BMS 208of FIG. 2 and the BMS 308 of FIG. 3A may be the same or equivalentcircuits. The component numbers in the circuit of FIG. 3A are made toconform with their incorporation into FIG. 3A.

As shown in FIG. 3A, the BMS 308 may further include a cutoff circuit310 (e.g., MOSFET or other known transistor) and a driver IC 312, eachbeing coupled to the reverse bias protection circuit 314. The MOSFET 310may include a drain terminal 356 a (input), a gate terminal 356 b(control input, which may control the operating state of MOSFET 310),and a source terminal 356 c (output). The drain terminal or input 356 amay be directly coupled to a positive terminal of a battery pack (notshown in FIG. 3A) via a positive supply line 352. The gate terminal orcontrol input 356 b may be coupled to the driver IC 312 by way of thereverse bias protection circuit 314. The source terminal or output 356 cmay be directly coupled to the reverse bias protection circuit 314. Thesource terminal 356 c may further be directly coupled to a positivebattery output terminal 316 (also referred to herein as positiveterminal 316), and the positive terminal 316 is directly coupled to an(external) electrical load 306. The electrical load 306 may also bedirectly coupled to a negative battery output terminal of the batterypack via a ground return line 354. It will be appreciated that theelectrical load 306 may be located external to the battery pack (thatis, the electrical load 306 may not be part of the battery pack). Asfurther shown, various junctions of two or more electrical conductors orwires may be respectively represented by nodes 370 a, 370 b, 370 c, 370d, 370 e, 370 f, 370 g, 370 h, 370 i, 370 j, and 370 k. Dasheddirectional arrows 382 depict exemplary current flow during expectedswitching ON of the MOSFET 310 during normal circuit operation, asdescribed hereinbelow. That is, the directional arrows 382 depictexemplary current flow when the MOSFET 310 is in an ON state and alow-current leakage transistor 358 of the reverse bias protectioncircuit 314 is in the OFF state when reverse bias at the positiveterminal 316 is not present.

The MOSFET 310 may further include a body diode 356 d. In somecircumstances, for example, during a reversed polarity event or whensignificant negative electric noise has built up in the battery systemand the reverse bias protection circuit 314 is not present, a reversebias voltage may be applied across the body diode 356 d when the MOSFET310 is in an OFF state. The body diode 356 d may then be triggered,unexpectedly switching the MOSFET 310 from the OFF state to an ON state.

During such events where the reverse bias voltage is applied and thereverse bias protection circuit 314 is not present, a higher-currentprofile may develop in the battery system. Accordingly, a significantamount of energy may accumulate, and the accumulated energy maydissipate via a weakest (that is, least resistant) channel in thebattery system. For example, absent the reverse bias protection circuit314, a higher current may pass through the body diode 356 d to ground,thus overloading the MOSFET 310. Thus, the reverse bias protectioncircuit 314 is provided herein for controlling such higher currents. Asdiscussed in detail below, and as exemplified above with reference toFIG. 2 , the reverse bias protection circuit 314 may protect MOSFET 310from the reverse bias voltage by maintaining each of a V_(G) and a V_(S)of the MOSFET 310 near, or substantially at, 0 V. Accordingly, dotteddirectional arrows 384 depict exemplary current flow during reverse biasvoltage conditions, wherein current may be redirected through thereverse bias protection circuit 314, as described hereinbelow. That is,the directional arrows 384 depict exemplary current flow when the MOSFET310 is in an OFF state and the low-current leakage transistor 358 of thereverse bias protection circuit 314 is in the ON state. Thus, a currentpath is shown beginning at ground 366 and it passes through diodes 364 aand 364 b, through resistors 362 a and 362 b, through diode 364 d,through resistor 362 c, through transistor 358, through node 370 e, andending at the electrical load 306.

As shown, the driver IC 312 may be provided with three pins 368 a, 368b, and 368 c, such that timing of outputs therefrom may be varied.Specifically, the pin 368 a may be employed to turn ON the MOSFET 310,the pin 368 b may be employed to turn OFF the MOSFET 310, and the pin368 c may be employed as a reference pin for controlling a V_(GS) of theMOSFET 310. As such, the pin 368 a may provide a voltage (for example, 5V) that may be delivered to the gate terminal 356 b of the MOSFET 310 toswitch the MOSFET 310 ON, the pin 368 b may pull the V_(G) to ground,and the pin 368 c may be coupled to the source terminal 356 c of theMOSFET 310 to reference the V_(S). In some examples, a switchingmechanism of the pin 368 a may be slower than a switching mechanism ofthe 368 b. That is, a resistance of a resistor 362 a coupling betweenthe pin 368 a and the MOSFET 310 may be higher than a resistance of aresistor 362 b coupling between the pin 368 b and the MOSFET 310.

Absent the reverse bias protection circuit 314, when significantnegative V_(S) is applied, the V_(GS) may increase to a positive valueabove a V_(th) of the MOSFET 310. However, the reverse bias protectioncircuit 314 may protect the MOSFET 310 by maintaining the V_(G) and theV_(S) near, or substantially at, 0 V, thereby maintaining an OFF stateof the MOSFET 310. Two principal features of the reverse bias protectioncircuit 314 may be provided to protect various components of the BMS308, and thereby of the battery system as a whole: diodes 364 a, 364 b,and 364 f to feed current from ground 366, and the low-current leakagetransistor 358 to maintain the V_(GS) of the MOSFET 310 below the V_(th)(as shown by the directional arrows 384).

For example, when the reverse bias voltage is applied, the diode 364 fmay prevent excess current from draining from the pin 368 c to thesource terminal 356 c of the MOSFET 310 via a resistor 362 g coupledtherebetween. Specifically, the current may instead be fed from ground366 via the diode 364 f, as shown by the directional arrows 384. Asshown, in some examples, the diode 364 f may be a Schottky diode, asSchottky diodes may have a relatively low forward voltage drop, suchthat the diode 364 f may be closer to ground 366. Further, configuringthe diode 364 f to be oriented as shown may block current from flowingback to ground 366 when the MOSFET 310 controllably switched to the ONstate. Additionally, resistors 362 f and 362 g may be provided inparallel to limit current flow from the pin 368 c, maintaining a voltageof the pin 368 c near zero when the negative V_(S) is detected and neara reference value during expected battery operation. When the MOSFET 310is OFF, due to the inductive feature of the electrical load 306, currentmay continue to flow through the positive terminal 316 to the electricalload 306. Accordingly, the node 370 j may have a negative voltage. Inorder to sustain the current flow to the electrical load 306 and notdrain current from the pin 368 c, the diode 364 f and the node 370 i areprovided to form a new circuit path to provide the current to theelectrical load 306.

Similarly, and as further shown, the diodes 364 a and 364 b may becoupled in series to prevent excess current from draining from thecharge pump 320 within the driver IC 312 to the gate terminal 356 b ofthe MOSFET 310 via the pin 368 a and the resistor 362 a coupledtherebetween. Specifically, a current may instead be fed from ground 366via the diodes 364 a and 364 b when a negative V_(S) is unexpectedlydetected, as shown by the directional arrows 384. As such, the diodes364 a and 364 b may be low-leakage diodes, providing low leakage currentduring unexpected battery operation. In this way, a controllability ofthe battery system by the driver IC 312, and thereby the BMS 308, may beprotected. Further, configuring the diodes 364 a and 364 b to beoriented as shown may block current from flowing back to ground 366 whenthe current is provided by the charge pump 320 in response to a switchON request at the driver IC 312, as shown by the directional arrows 382.

In some examples, and as further shown, the driver IC 312 may becommunicably coupled to a controller 372, which may store machinereadable instructions on a non-transitory storage device, theinstructions executable by the controller 372 to enable variousfunctionalities of the BMS 308, such as receiving and transmittingswitching requests, monitoring the battery system, etc. It will beappreciated that, though the controller 372 is depicted in FIG. 3A asbeing included within the driver IC 312, in other examples, thecontroller 372 may be positioned external to the driver IC 312.

When a reverse bias voltage, that is, a negative V_(S), is detected atthe source terminal 356 c of the MOSFET 310, a generated current may befed towards node 370 f and the low-current leakage transistor 358 fromground 366 through the diode 364 f (for example, via the resistor 3620.In some examples, the diode 364 e may be a Zener diode or atransient-voltage suppression (TVS) diode, such that the diode 364 e mayclamp a voltage thereacross at a set value, such as 8.5 V.

In some examples, the low-current leakage transistor 358 may be a BJTincluding an input (e.g., collector) terminal 360 a, a control input(e.g., base) terminal 360 b, and an output (e.g., emitter) terminal 360c. A voltage of approximately 8.5 volts relative to the source voltageV_(S) may be generated at node 370 f via diode 364 e, this voltage maybe lowered via a voltage divider formed by resistors 362 e and 362 dallowing current to flow into the base terminal 360 b, thereby switchingtransistor 358 from an OFF state to an ON state.

As shown, an anode of the diode 364 e may be coupled to the emitterterminal 360 c and a cathode of the diode 364 e may be directly coupledto the node 370 f. As such, the anode of the diode 364 e may be a highervoltage than that of the emitter terminal 360 c, and the diode 364 e mayfunction to stabilize a base-emitter voltage (V_(BE)) of the low-currentleakage transistor 358.

Accordingly, when the negative V_(S) is unexpectedly generated, thelow-current leakage transistor 358 may switch ON via the negative V_(S)increasing the V_(BE) thereof. Thus, the low-current leakage transistor358 may be considered a switch that allows current to flow from diodes364 a and 364 b toward the source terminal 356 c as indicated by thedirectional arrows 384. The current may flow through resistor 362 a toresistor 362 b, then to diode 364 d, then to resistor 362 c, thenthrough transistor 358 before reaching node 370 k, which is directlycoupled to the source terminal 356 c. The current flow allows V_(G) toapproach V_(S), thereby preventing MOSFET 310 from switching ON.

Specifically, once the low-current leakage transistor 358 is ON, theV_(G) of the MOSFET 310 may be quickly dragged down to an emittervoltage (VE) of the low-current leakage transistor 358. Since theemitter terminal 360 c may be coupled to the source terminal 356 c ofthe MOSFET 310, the V_(GS) of the MOSFET 310 may be maintained via aV_(CE) of the low-current leakage transistor 358. Accordingly, when theV_(CE) drops across the collector terminal 360 a and the emitterterminal 360 c, for example, to less than 1 V, the V_(GS) may bemaintained at a value less than the V_(th), and the MOSFET 310 mayremain in the OFF state.

On the other hand, during expected battery operation, the low-currentleakage transistor 358 may be switched OFF, and the pin 368 a may supplyvoltage to raise V_(G) of the MOSFET 310 to switch MOSFET 310 ON.Electric current may flow from the drain terminal 356 a to the sourceterminal 356 c and to the electrical load 306 when MOSFET 310 isswitched ON. MOSFET 310 may be switched OFF via pin 368 b. Electriccurrent flow from the drain terminal 356 a to the source terminal 356 cmay be prevented when MOSFET 310 is switched to ON. In this way, aswitchable current path including the low-current leakage transistor 358may be electrically coupled to the MOSFET 310, the switchable currentpath being arranged between the gate terminal 356 b of the MOSFET 310and the source terminal 356 c of the MOSFET 310.

In some examples, diodes 364 c and 364 d may further be provided asblocking diodes to maintain a direction of current flow to the driver IC312 via the pin 368 b and to the low-current leakage transistor 358 viathe resistor 362 c, respectively. Accordingly, and as shown, the diode364 c may be oriented in a desired direction of current being passed tothe driver IC 312 via the pin 368 b when the MOSFET 310 is controllablyswitched OFF, and the diode 364 d may be oriented in a desired directionof current being passed to the low-current leakage transistor 358 viathe resistor 362 c to protect the MOSFET 310 from an unexpected reversebias voltage passed to the source terminal 356 c. In one example, eachof the diodes 364 c and 364 d may be a diode with a relatively lowforward voltage drop, such as a Schottky diode.

In this way, a current may flow from the nodes 370 b and 370 c coupledto the gate terminal 356 b of the MOSFET 310 to the nodes 370 d and 370e coupled to the source terminal 356 c of the MOSFET 310 in response toa negative V_(S) being applied to the node 370 e while current flowacross the gate terminal 356 b to the source terminal 356 c isprevented. Thus, a negative voltage at the source terminal 356 c mayprevent the MOSFET 310 from turning ON. Such current flow may be enabledby activating the low-current leakage transistor 358 disposed betweenthe nodes 370 b and 370 c and the nodes 370 d and 370 e. In someexamples, the current may flow from ground 366 through the diodes 364 aand 364 b to the nodes 370 b and 370 c. However, the current may notflow from the nodes 370 b and 370 c to the nodes 370 d and 370 e inresponse to an absence of the negative V_(S) being applied to the node370 e.

In some examples, the circuitry depicted by schematic diagram 300 may beimplemented in a vehicle battery system to prevent turn ON of the MOSFET310 even when a switch ON request is received. As an example, the MOSFET310 may be one of a plurality of MOSFETs arranged in an array. Each ofthe MOSFETs 310 may be electrically coupled to one of a plurality oflithium-ion battery cells in the battery pack. In some examples, when aswitch ON request is received, a portion of the lithium-ion batterycells may be utilized to provide power to the vehicle battery system,and a remaining portion may be kept OFF by the reverse bias protectioncircuit 314.

As shown by the directional arrows 382 and 384, whether the MOSFET 310is switched ON or switched OFF in response to the negative V_(S) beingapplied to the node 370 e, the current may pass along a line 394 andacross each of the positive terminal 316 and the electrical load 306 tothe ground return line 354, wherefrom the current may be cycled backalong a line 386. As further described below with reference to FIG. 3B,each of the ground return line 354 and the line 386 may be coupled to adiode array. Specifically, the diode array may form, with the electricalload 306, a short-circuit protection circuit which may cycle anddissipate accumulated current in the vehicle battery system when theMOSFET 310 is maintained OFF by the reverse bias protection circuit 314.

Referring now to FIG. 3B, a schematic diagram 350 depicting circuitry ofone example of a short-circuit protection circuit 390 is shown. It willbe appreciated that components of the short-circuit protection circuit390 may be included in, or coupled to, the BMS 308 described above withreference to FIG. 3A. Accordingly, in some examples, one or morecomponents described with reference to FIG. 3B may be substituted intothe vehicle battery system described above with reference to FIG. 2 .The component numbers in the circuit of FIG. 3B are made to conform withtheir incorporation into FIG. 3B.

As shown in FIG. 3B, the short-circuit protection circuit 390 mayinclude a diode array 334. The diode array 334 may be an array offlyback or freewheeling diodes arranged in parallel. As shown, anodes ofall diodes in the diode array 334 may be directly coupled together andcathodes of all diodes in the diode array 334 may be directly coupledtogether. Though four individual diodes are shown in the schematicdiagram 350 as being included within the diode array 334, it will beappreciated that FIG. 3B depicts an exemplary embodiment, and should beunderstood as non-limiting. Accordingly, a total number of diodes in thediode array 334 may be less than, equal to, or greater than four.

The electrical load 306, characterized by an inductance 374 a and aresistance 362 h, may be coupled to the diode array via the positivebattery output terminal 316 and a negative battery output terminal 318(also referred to herein as negative terminal 318). Specifically, thediode array 334 may be electrically coupled to the positive terminal 316via a line 386 and the negative terminal 318 via a line 388. Further,the electrical load 306 may be coupled to the positive terminal 316 viaa line 392 and the negative terminal 318 via the ground return line 354,such that the short-circuit protection circuit 390 may be formed betweenthe diode array 334 and the electrical load 306.

Dashed directional arrows 396 depict exemplary current flow followingexpected switching ON of the MOSFET 310 (described above with referenceto FIG. 3A) during normal circuit operation. Specifically, a current mayflow from the source terminal 356 c (described above with reference toFIG. 3A) of the MOSFET 310 to the positive terminal 316 via the line394, wherefrom the current may flow across the electrical load 306 topower a battery-powered system. From the electrical load 306, thecurrent may flow along the ground return line 354 from the electricalload 306 to the negative terminal 318 and on to a battery pack (notshown at FIG. 3B). In this way, during normal circuit operation, aclosed circuit may be formed between the battery pack, the MOSFET, andthe electrical load.

Dotted directional arrows 398 depict exemplary current flow during ashort-circuit condition, where the MOSFET 310 (described above withreference to FIG. 3A) is opened or turned OFF. During such conditions,the current may not flow to the battery pack, and may instead cycleacross the electrical load 306 and the diode array 334. That is, thedirectional arrows 398 depict current flow when the MOSFET 310 ismaintained in an OFF state by the reverse bias protection circuit 314(described above with reference to FIG. 3A). The current may flow fromthe reverse bias protection circuit 314 to the positive terminal 316 viathe line 394, wherefrom the current may flow to the electrical load 306.Specifically, the current may flow from ground 366 to a lower voltagethat forms at the positive terminal 316. The lower voltage may begenerated when the MOSFET 310 is opened. For example, when the MOSFET310 is opened to cease current flow to the electrical load 306, theinductance 374 a attempts to maintain current flow via inducing avoltage opposite in polarity to the voltage of the positive and negativeterminals 316, 318 when the MOSFET 310 is closed or ON. From theelectrical load 306, the current may flow along the ground return line354 to the negative terminal 318.

Because the inductance 374 a of the electrical load 306 attempts tomaintain the current flow via inducing the voltage that is opposite inpolarity, the diode array 334 becomes forward biased, thereby allowingthe current flow from the negative terminal 318 to the positive terminal316. Thus, in response to the short-circuit condition, a low-resistancepath may be provided by the diode array 334, which may recirculateexcess current within the electrical load 306. In this way, by couplingthe source terminal of the MOSFET to the short-circuit protectioncircuit including the array of freewheeling diodes, the positiveterminal, the electrical load, and the negative terminal, the MOSFET maybe protected from degradation (for example, due to entering avalanchemode when the MOSFET is conducted in an OFF state), as the excesscurrent may be redirected by the short-circuit protection circuit.

As further shown, the lines 386, 388 may be respectively characterizedby parasitic inductances 374 b, 374 c. As described in detail below withreference to FIG. 6 , the parasitic inductances 374 b, 374 c may be atleast partially mitigated via busbars (not shown at FIG. 3B)respectively coupling the positive terminal 316 to the line 386 and thenegative terminal 318 to the line 388. Accordingly, by reducing theparasitic inductances 374 b, 374 c via the busbars, the current may moreeasily be redirected along the directional arrows 398 and across thediode array 334. In some examples, a shunt resistor (not shown at FIG.3B) may further be disposed along the ground return line 354 between thebattery pack and the negative terminal 318 to further aid in redirectingthe current along the directional arrows 398 and across the diode array334.

Referring now to FIG. 4 , a flow chart depicting a method 400 forproviding reverse bias and short-circuit protection to a battery cutoffcircuit is shown. The reverse bias and short-circuit protection may beprovided via the circuitry illustrated in FIGS. 2-3B. In general, duringapplication of a reverse bias voltage in a vehicle battery system, suchas due to an unintentional reversed polarity event or built-up negativeelectric noise, the cutoff circuit may be at risk of unintentionalswitch-on. In specific examples where the cutoff circuit is a MOSFET, ifa V_(GS) of the MOSFET increases above a V_(th) of the MOSFET (forexample, via a sufficiently negative V_(S)), then the MOSFET mayunintentionally switch ON, potentially discharging and degrading thevehicle battery system. Further, even when the MOSFET is switched OFF,the MOSFET may still be conducting if a breakdown voltage thereof isreached due to a short-circuit condition and the MOSFET may enteravalanche mode, potentially degrading the MOSFET and thereby the vehiclebattery system. Accordingly, the method provided herein may detect theshort-circuit condition, switch the MOSFET OFF, confirm that the MOSFETis OFF by flowing current through a reverse bias protection circuit, anddissipate accumulated energy through a short-circuit protection circuit.

Method 400 is described below with regard to the systems and componentsdepicted in FIGS. 1A-3B. For example, in some examples, method 400 maybe implemented in the BMS 208 of FIG. 2 or the BMS 308 of FIG. 3A (andFIG. 3B). In such examples, steps of method 400, or a portion thereof,may represent actions taken via hardware devices, such as one or morecomponents of the BMS 208 or the BMS 308, in the physical world. It willbe appreciated that method 400 may be implemented with other systems andcomponents without departing from the scope of the present disclosure.It will further be appreciated that individual steps discussed withreference to method 400 may be added, removed, substituted, orinterchanged within the scope of the present disclosure.

Method 400 may begin at 402 of FIG. 4 , where method 400 may includeresponding to detection of a reverse bias voltage at a positive batteryterminal or to unintended switch ON of the cutoff circuit. If thereverse bias voltage or unintended switch ON is not detected, desiredbattery operation may proceed. Specifically, method 400 may proceed to404, where method 400 may include determining whether a switch ONrequest is received at the driver IC or at a controller coupled to thedriver IC. Specifically, the switch ON request may be a command toswitch the cutoff circuit of the BMS from an OFF state to an ON state.If the switch ON request is not received, method 400 may return to 402.

If the switch ON request is received, method 400 may proceed to 406,where method 400 may include turning ON a battery pack to power avehicle by switching ON the cutoff circuit of the BMS and closing abattery circuit of the vehicle battery system. Specifically, a positivesupply line may provide power from the battery pack to an (external)electrical load of the vehicle. However, it will be appreciated that thereverse bias protection circuit may mitigate degradation to the vehiclebattery system even when the switch ON request is received, for example,when negative electric noise builds up in the vehicle battery system.

At 408, method 400 may include determining whether a current detected bya current detection circuit of the BMS is greater than a thresholdcurrent. In some examples, the threshold current may be selected tomaintain an expected lifetime of the cutoff circuit. Specifically, thethreshold current may be less than or equal to a maximum currentmanageable by the cutoff circuit without excess degradation thereto(e.g., degradation beyond expected degradation resulting from normalbattery operation over a lifetime of the cutoff circuit). In someexamples, the current may be a first current flowing along the positivesupply line between the battery pack and the cutoff circuit.

If the detected current is determined to be less than or equal to thethreshold current, method 400 may proceed to 410 to maintain currentvehicle battery system operating conditions. Specifically, the vehiclebattery system may continue to provide power to the vehicle until aswitch OFF request is received. Method 400 may then end.

If the detected current is determined to be greater than the thresholdcurrent at 408, or if the reverse bias voltage or unintended switch ONis detected at 402, protection of battery operation may proceed. Inparticular, the reverse bias protection circuit may prevent the cutoffcircuit from coupling the battery cells to the electrical load, therebymitigating degradation to the vehicle battery system. Further, theshort-circuit protection circuit may cycle and dissipate accumulatedenergy across the external load to further mitigate degradation to thevehicle battery system by preventing the cutoff circuit from reachingthe breakdown voltage.

Method 400 may proceed to 412, where method 400 may include feeding acurrent (for example, a second current from ground) towards the outputof the cutoff circuit via a low-current leakage transistor in thereverse bias protection circuit. In some examples, the low-currentleakage transistor may be a BJT and the cutoff circuit may be a MOSFET,such that a collector terminal thereof may be coupled to a gate terminal(control input) of the MOSFET and an emitter terminal thereof may becoupled to the source terminal (output) of the MOSFET. The emitterterminal of the low-current leakage transistor may further be coupled toan anode of a Zener diode, and a base terminal of the low-currentleakage transistor may be coupled to a cathode of the Zener diode. Inother examples, a TVS diode may be employed.

At 414, method 400 may include increasing a V_(BE) of the low-currentleakage transistor via the Zener diode to switch ON the low-currentleakage transistor. Further, by respectively coupling the cathode andthe anode of the Zener diode to the base terminal and the emitterterminal of the low-current leakage transistor, the V_(BE) may beclamped to a set value, for example, less than 8.5 V.

At 416, method 400 may include maintaining the cutoff circuit in the OFFstate via reducing a WE of the low-current leakage transistor.Specifically, once the low-current leakage transistor is switched ON, avoltage across the collector and emitter terminals (that is, the WE) maydecrease to and be maintained at a low value, for example, less than 1V. Accordingly, by coupling the control input of the cutoff circuit tothe collector terminal of the low-current leakage transistor and theoutput of the cutoff circuit to the emitter terminal of the low-currentleakage transistor, a voltage difference between the control input ofthe cutoff circuit and the output of the cutoff circuit may becorrespondingly maintained. In examples wherein the cutoff circuit is aMOSFET, the gate terminal of the MOSFET may be coupled to the collectorterminal of the low-current leakage transistor, and the source terminalof the MOSFET may be coupled to the emitter terminal of the low-currentleakage transistor. The V_(GS) may be maintained via activating atransistor. In this way, the V_(GS) may be maintained below a V_(th) ofthe MOSFET, such that the MOSFET may be maintained in the OFF state.

At 418, method 400 may include cycling the current (for example, each ofthe first and second currents) across the external load and a diodearray in the short-circuit protection circuit. Specifically, the emitterterminal of the low-current leakage transistor may further be coupled tothe diode array, where the diode array may include a plurality offlyback or freewheeling diodes to provide a low-resistance path forredirecting the current away from the drain terminal of the MOSFET.

At 420, method 400 may include determining whether an excess current hasdissipated. In one example, the excess current may be an amount ofcurrent in the vehicle battery system exceeding the threshold current.If the excess current has not dissipated, method 400 may return to 418.If the excess current has dissipated, method 400 may return to 402. Itwill be appreciated that, even when the excess current has dissipated,the current may continue to cycle across the external load and the diodearray until a switch ON request is received (for example, at 404).

Referring now to FIG. 5A, a timeline 500 depicting first and secondexample operating sequences of the vehicle battery system of FIGS. 1A-3Bis shown. Specifically, the vehicle battery system may be configuredwith one or more cutoff circuits, such as one or more MOSFETs, coupledto one or more protection circuits. A given cutoff circuit may switch ONresponsive to a switch ON request received by the vehicle batterysystem, which may allow current to flow through the given cutoff circuitto power a vehicle in which the vehicle battery system may beimplemented. However, in some examples, the given cutoff circuit may bein an OFF state when a reverse bias voltage is applied to an output ofthe given cutoff circuit. In such examples, a protection circuit coupledto the given cutoff circuit may include a low-current leakagetransistor, such as a bipolar junction transistor (BJT). When switchedON, the low-current leakage transistor may be configured to maintain avoltage applied across a control input and an output of the given cutoffcircuit, such that the given cutoff circuit is not unintentionallyswitched ON. In this way, the protection circuit may mitigatedegradation to the vehicle battery system by reducing a possibility ofunintentional activation of the cutoff circuitry. In some examples, thevehicle battery system may include the BMS 208 or the BMS 308respectively described above with reference to FIGS. 2 and 3A.

Timeline 500 depicts a cutoff circuit state at solid curves 501 and 503,a voltage applied to the output (e.g., source) of the cutoff circuit atsolid curves 511 and 513, a voltage difference between the control inputof the cutoff circuit and the output of the cutoff circuit at solidcurves 521 and 523, a low-current leakage transistor state at solidcurves 531 and 533, a V_(BE) of the low-current leakage transistor atsolid curves 541 and 543, and a V_(CE) of the low-current leakagetransistor at solid curves 551 and 553. Additionally, dashed curves 522and 524 represent a first threshold voltage for the voltage appliedacross the control input and the output at which the cutoff circuitstate may switch between an OFF state and an ON state. It will beappreciated that, when the cutoff circuit includes a MOSFET, the voltageapplied to the output (curves 511 and 513) may be a V_(S) of the MOSFET,the voltage difference across the control input and the output (curves521 and 523) may be a V_(GS) of the MOSFET, and the first thresholdvoltage (curves 522 and 524) may be a V_(th) of the MOSFET.

All curves are depicted over time and plotted along an abscissa, wheretime increases from left to right of the abscissa. Further, a dependentvariable represented by each curve discussed above is plotted along arespective ordinate, where the dependent variable increases from bottomto top of the given ordinate (unless otherwise stated or shown).

At t1, the first example operating sequence of the vehicle batterysystem may begin. Between t1 and t2, each of the cutoff circuit state(curve 501) and the low-current leakage transistor state (curve 531) maybe an OFF state. At t2, a negative voltage may be detected at the outputof the cutoff circuit (curve 511), for example, due to a reverse biasvoltage condition. In response to the negative voltage being detected atthe output, a current may be redirected to a Zener diode (or a TVSdiode) coupled to the low-current leakage transistor.

At t3, the low-current leakage transistor may switch from the OFF stateto the ON state (curve 531). The current may thus flow through thelow-current leakage transistor instead of the cutoff circuit, as thelow-current leakage transistor may be coupled to a current path of lowerresistance than the cutoff circuit.

Accordingly, after t3, the WE may decrease significantly from a firstvalue to a second value and then be maintained at the second value(curve 551). For example, the WE may decrease from about 12 V to lessthan 1 V (e.g., near, or substantially at, 0 V) and then be maintainedthereat. Further, the V_(BE) may increase and level off at a value lessthan a value clamped by the Zener diode (curve 541). For example, V_(BE)may increase to about 0.7 V. Moreover, in the vehicle battery systemcorresponding to the depicted example, the control input of the cutoffcircuit may be coupled to a collector terminal of the low-currentleakage transistor, and the output of the cutoff circuit may be coupledto an emitter terminal of the low-current leakage transistor.Accordingly, the voltage difference across the control input and theoutput may be maintained (curve 521), e.g., less than the firstthreshold voltage (curve 522). For example, the voltage differenceacross the control input and the output may be correspondinglymaintained at less than 1 V (e.g., near, or substantially at, 0 V). Inthis way, the protection circuit may prevent the voltage differenceacross the control input and the output from reaching the firstthreshold voltage, such that the cutoff circuit may remain in the OFFstate (curve 501). Between t3 and t4, an extended time interval isindicated by a break in the abscissa during which a cause of thenegative voltage at the output of the cutoff circuit, such as thereverse bias voltage condition, may end.

At t4, the second example operating sequence of the vehicle batterysystem may begin. Accordingly, between t4 and t5, each of the cutoffcircuit state (curve 503) and the low-current leakage transistor state(curve 533) may be the OFF state.

At t5, a switch ON request may be received by the vehicle battery systemfor the cutoff circuit, and a voltage may be applied to the controlinput of the cutoff circuit. Thus, between t5 and t6, the voltagedifference across the control input of the cutoff circuit and the outputof the cutoff circuit may increase (curve 523) until, at t6, the firstthreshold voltage is reached (curve 524) and the cutoff circuit switchedfrom the OFF state to the ON state. The voltage difference across thecontrol input and the output may continue to increase to a constantvoltage value. Correspondingly, after t6, the voltage applied to theoutput of the cutoff circuit may increase to a constant (positive)voltage value (curve 513).

During the second example operating sequence, each of the V_(BE) and theV_(CE) of the low-current leakage transistor remain at constant voltagevalues near, or substantially at, 0 V (curves 543 and 553,respectively). Accordingly, the V_(BE) does not reach the secondthreshold voltage (curve 544) during the second example operatingsequence, and the low-current leakage transistor remains in the OFFstate (curve 533). In this way, in some examples, the protection circuitmay not be activated in response to the vehicle battery system receivinga switch ON request for the cutoff circuit.

Referring now to FIG. 5B, a timeline 550 depicting a third exampleoperating sequence of the vehicle battery system of FIGS. 1A-3B isshown. Specifically, the vehicle battery system may be configured withone or more cutoff circuits, such as one or more MOSFETs, coupled to oneor more protection circuits. A given cutoff circuit may switch ONresponsive to a switch ON request received by the vehicle batterysystem, which may allow current to flow through the given cutoff circuitto power a vehicle in which the vehicle battery system may beimplemented. However, in some examples, the given cutoff circuit may beswitched to an OFF state in response to a short circuit condition beingdetected. In such examples, a protection circuit coupled to the givencutoff circuit may include a low-current leakage transistor, such as aBJT. When switched ON, the low-current leakage transistor may beconfigured to reduce and maintain a voltage applied at a control inputand an output of the given cutoff circuit, such that the given cutoffcircuit is not unintentionally switched ON. The protection circuit mayfurther include a diode array, such as an array of flyback orfreewheeling diodes, coupled to each of the low-current leakagetransistor and an external load. In this way, the protection circuit maymitigate degradation to the vehicle battery system during ashort-circuit condition by cycling and dissipating excess current acrossthe diode array and the external load while maintaining the cutoffcircuit in the OFF state. In some examples, the vehicle battery systemmay include the BMS 208 described above with reference to FIG. 2 or theBMS 308 described above with reference to FIG. 3A (and FIG. 3B).

Timeline 550 depicts a cutoff circuit state at a solid curve 506, acurrent detected by the BMS at a solid curve 566, a voltage differencebetween an input and the output of the cutoff circuit at a solid curve576, a voltage difference across the diode array (that is, a voltagedifference between cathodes and anodes of the array of freewheelingdiodes) at solid curve 586, a low-current leakage transistor state at asolid curve 536, a V_(BE) of the low-current leakage transistor at asolid curve 546, and a WE of the low-current leakage transistor at asolid curve 556. Additionally, a dashed curve 567 represents a thresholdcurrent at which a switch OFF may be generated for the cutoff circuitand a dashed curve 577 represents a breakdown voltage of the cutoffcircuit above which the cutoff circuit may enter avalanche mode. It willbe appreciated that, when the cutoff circuit includes a MOSFET, thevoltage difference across the input and the output (curve 576) may be adrain-source voltage (VDs) of the MOSFET.

All curves are depicted over time and plotted along an abscissa, wheretime increases from left to right of the abscissa. Further, a dependentvariable represented by each curve discussed above is plotted along arespective ordinate, where the dependent variable increases from bottomto top of the given ordinate (unless otherwise stated or shown).

At t7, the third example operating sequence of the vehicle batterysystem may begin. Between t7 and t8, the cutoff circuit state (curve506) may be the ON state and the low-current leakage transistor state(curve 536) may be the OFF state. Just before t8, the detected currentmay increase (curve 566) towards the threshold current (curve 567) as aresult of a short-circuit condition in the vehicle battery system.Concomitantly, the voltage difference across the input and the output ofthe cutoff circuit may increase (curve 576).

In response to the detected current (curve 566) reaching the thresholdcurrent (curve 567), at t8, the cutoff circuit may switch from the ONstate to the OFF state (curve 506) to prevent current flow thereacrossand drop the detected current. Further, in response to the cutoffcircuit switching OFF, a current may be redirected from ground to aZener diode (or a TVS diode) coupled to the low-current leakagetransistor.

As further shown at t8, the voltage difference across the diode arraymay decrease and dip below 0 V (curve 586), allowing the diode array toprovide a first current path of lower resistance than the cutoffcircuit. Accordingly, excess current accumulated in the vehicle batterysystem as a result of the short-circuit condition may be redirected tothe first current path. In this way, current may cycle and dissipateacross the diode array and the external load coupled thereto after thecutoff circuit is switched OFF.

At t9, the low-current leakage transistor may switch from the OFF stateto the ON state (curve 536). The current may thus flow through thelow-current leakage transistor instead of the cutoff circuit, as thelow-current leakage transistor may be coupled to a second current pathof lower resistance than the cutoff circuit. The current may thencontinue to flow from the low-current leakage transistor to the diodearray.

After t9, the WE may decrease significantly (curve 556), for example,from about 12 V to less than 1 V, near 0 V, or substantially 0 V.Further, the V_(BE) may increase and level off at a value clamped by theZener diode (curve 546). For example, V_(BE) may increase to about 0.7V. Further, in the vehicle battery system corresponding to the depictedexample, the control input of the cutoff circuit may be coupled to acollector terminal of the low-current leakage transistor, and the outputof the cutoff circuit may be coupled to an emitter terminal of thelow-current leakage transistor. Correspondingly, the voltage differenceacross the control input and the output may decrease in magnitude toless than 1 V, to near 0 V, or to substantially 0 V. In this way, theprotection circuit may prevent the voltage difference across the controlinput and the output from reaching the first threshold voltage, suchthat the cutoff circuit may remain in the OFF state (curve 506).

Further, as a result of current redirection and dissipation provided bythe diode array and the external load, the voltage difference across theinput and the output of the cutoff circuit (curve 576) may level off.Additionally, since the cutoff circuit is in the OFF state (curve 506),the voltage difference across the diode array (curve 586) may also leveloff at a positive value (though the current may continue to flow to thediode array from the low-current leakage transistor). Specifically,because the cutoff circuit is maintained open by current redirection tothe low-current leakage transistor via the second current path and thevoltage difference across the input and the output thereof is maintainedbelow the breakdown voltage (curve 577) by current redirection to thediode array via the first current path, additional current from thebattery pack is restricted (e.g., substantially restricted) from flowingacross the cutoff circuit, and the voltage difference across the diodearray stabilizes. In this way, the protection circuit may prevent thevoltage difference across the input and the output of the cutoff circuitfrom reaching the breakdown voltage, thereby preventing the cutoffcircuit from entering avalanche mode when switched OFF.

Referring now to FIG. 6 , a schematic diagram 600 depicting a printedcircuit board assembly (PCBA) 624 is shown. The PCBA 624 may include aprinted circuit board (PCB) 626 having various electronics componentsprinted, soldered, or otherwise affixed thereon. In one example, thePCBA 624 may implement a BMS, such as the BMS 208 describe above withreference to FIG. 2 or the BMS 308 described above with reference toFIG. 3A (and FIG. 3B). As such, the PCBA 624 may include variouscircuits and electronics components operable to monitor a batterysystem. For example, the PCBA 624 may include a cutoff circuit formedfrom an array of MOSFETs 610, where inputs and outputs of the MOSFETs610 may be coupled to a first busbar 628 a and a second busbar 628 b,respectively. The PCBA 602 may further include an array of flyback orfreewheeling diodes 634 where cathodes and anodes of the freewheelingdiodes 634 may be coupled to the second busbar 628 b and a third busbar628 c, respectively. It will further be appreciated that additionalelectronics components may be printed, soldered, or otherwise affixed ona side of the PCB 626 opposite to a side of the PCB 626 depicted in FIG.6 . As a non-limiting example, the array of freewheeling diodes 634 mayinclude two freewheeling diodes on one side of the PCB 626 (as shown inFIG. 6 ) and two freewheeling diodes on an opposite side of the PCB 626(not shown in FIG. 6 ).

As shown, the busbars 628 a, 628 b, 628 c may respectively includecouplings 630 a, 630 b, 620 c. The couplings 630 a, 630 b, 630 c may beindependently configured to couple (directly or via electricalconductors) the busbars 628 a, 628 b, 628 c to battery terminals (forexample, electrode tabs, terminal posts, etc.; not shown at FIG. 6 ) ofthe battery system. As a first example, the first busbar 628 a maycouple a positive supply line of the battery pack to the inputs of thearray of MOSFETs 610 via the coupling 630 a. As a second example, thesecond busbar 628 b may couple a positive terminal post to each of theoutputs of the array of MOSFETs 610 and each of the cathodes of thearray of freewheeling diodes 634 via the coupling 630 b. As a thirdexample, the third busbar 628 c may couple a negative terminal post toeach of the anodes of the array of freewheeling diodes 634 via thecoupling 630 c. Each of the first and second busbars 628 a, 628 b may becoupled to one or more MOSFETs 610 in the array of MOSFETs 610, suchthat when the one or more MOSFETs 610 are switched ON, a circuit betweena given pair of battery terminals may be closed.

The busbars 628 a, 628 b, 628 c may further include pins 636 a, 636 b,636 c, respectively. The pins 636 a, 636 b, 636 c may respectivelycouple the busbars 628 a, 628 b, 628 c to the various electronicscomponents included in the PCBA 624. As a first example, the pins 636 amay independently directly couple the first busbar 628 a to each of theinputs of the array of MOSFETs 610. As a second example, the pins 636 bmay independently directly couple the second busbar 628 b to each of theoutputs of the array of MOSFETs 610 and the cathodes of the array offreewheeling diodes 634. As a third example, the pins 636 c mayindependently directly couple the third busbar 628 c to each of theanodes of the array of freewheeling diodes 634. The pins 636 a, 636 b,636 c may further function as shunts to distribute current and mayrespectively structurally stabilize the busbars 628 a, 628 b, 628 c.

Dashed directional arrows 696 depict exemplary current flow when thecutoff circuit is in an ON state. Specifically, and as shown by thedirectional arrows 696, the BMS may be configured to sequentially flow acurrent from the first busbar 628 a to the second busbar 628 b to thethird busbar 628 c when the cutoff circuit is in the ON state, such thatthe current may directed across the electrical load to the battery pack,and not the array of freewheeling diodes 634.

Further, dotted directional arrows 698 depict exemplary current flowwhen the cutoff circuit is in an OFF state. Specifically, and as shownby the directional arrows 698, the BMS may be configured to flow thecurrent from the third busbar 826 c to the second busbar 628 b when thecutoff circuit is in the OFF state, such that the current may beredirected across the array of freewheeling diodes 634.

The busbars 628 a, 628 b, 628 c may be further configured to reduceparasitic inductances present in the battery system. As a first example,the first busbar 628 a may be configured to reduce a parasiticinductance between the battery pack and the array of MOSFETs 610. As asecond example, the second busbar 628 b may be configured to reduce aparasitic inductance between the cathodes of the array of freewheelingdiodes 634 and the positive terminal post. As a third example, the thirdbusbar 628 c may be configured to reduce a parasitic inductance betweenthe anodes of the array of freewheeling diodes 634 and the negativeterminal post. In this way, the battery system may include a pluralityof busbars for redirecting and distributing current during both expectedand unexpected operations of the battery system

In this way, a vehicle battery system including a battery pack coupledto a battery management system (BMS) is provided, where the BMS mayinclude a reverse bias protection circuit for maintaining a cutoffcircuit in an OFF state during an unexpected voltage condition and atleast some components of a short-circuit protection circuit for cyclingand dissipating excess current generated via the unexpected voltagecondition. The BMS may further include a current detection circuit fordetecting excess or anomalous current flow indicative of the unexpectedvoltage condition. In some examples, the cutoff circuit may include ametal-oxide-semiconductor field-effect transistor (MOSFET).Specifically, the reverse bias protection circuit may maintain agate-source voltage (V_(GS)) of the MOSFET below a threshold voltage(V_(th)) unless both the current detected by the current detectioncircuit has dissipated via the short-circuit protection circuit and aswitch ON request is received at the BMS. In some examples, theshort-circuit protection circuit may include a diode array coupledbetween positive and negative terminal posts of the battery pack, suchthat the diode array may further be coupled to an electrical load of thevehicle battery system. Accordingly, the diode array may provide alow-resistance path for current dissipation by permitting cyclingthereacross and across the electrical load. A technical effect ofproviding both the reverse bias protection circuit and the short-circuitprotection circuit is that the MOSFET may be both maintained OFF andprevented from entering avalanche mode during application of a reversebias voltage or during a short-circuit event. Accordingly, the MOSFET,and thereby the vehicle battery system as a whole, may be protected fromdegradation during the unexpected voltage condition.

In one example, a vehicle battery system comprises a battery managementsystem comprising a MOSFET, a battery pack having a plurality of stackedbattery cells, a positive supply line of the battery pack being coupledto the MOSFET and a reverse bias protection circuit coupled to theMOSFET, the reverse bias protection circuit comprising a low-currentleakage transistor configured to maintain a gate-source voltage (V_(GS))of the MOSFET below a threshold voltage (V_(th)) of the MOSFET.

In another example, a vehicle battery system comprises a batterymanagement system (BMS) comprising a cutoff circuit electrically coupledto reverse bias protection circuit, and a battery pack having aplurality of stacked battery cells, a positive supply line of thebattery pack being electrically coupled to the cutoff circuit, andwherein the reverse bias protection circuit includes each of an inputelectrically coupled to a control input of the cutoff circuit, an outputelectrically coupled to an output of the cutoff circuit, and a controlinput electrically coupled to the output of the cutoff circuit. A firstexample of the vehicle battery system further includes wherein the inputof the reverse bias protection circuit, the output of the reverse biasprotection circuit, and the control input of the reverse bias protectioncircuit are included in a switchable current path of the reverse biasprotection circuit, the switchable current path arranged between thecontrol input of the cutoff circuit and the output of the cutoffcircuit. A second example of the vehicle battery system, optionallyincluding the first example of the vehicle battery system, furtherincludes wherein the BMS is configured to flow electric current throughthe switchable current path upon detection of a reverse bias voltage atthe output of the cutoff circuit, and wherein the BMS is furtherconfigured to prevent electric current flow through the switchablecurrent path in response to an absence of the reverse bias voltage atthe output of the cutoff circuit. A third example of the vehicle batterysystem, optionally including one or more of the first and secondexamples of the vehicle battery system, further includes wherein thereverse bias protection circuit comprises one or more diodes, the one ormore diodes configured to feed the electric current to the switchablecurrent path upon detection of the reverse bias voltage. A fourthexample of the vehicle battery system, optionally including one or moreof the first through third examples of the vehicle battery system,further includes wherein the input of the reverse bias protectioncircuit, the output of the reverse bias protection circuit, and thecontrol input of the reverse bias protection circuit are included in alow-current leakage transistor coupled to a Zener diode, the Zener diodeconfigured to switch ON the low-current leakage transistor by increasinga base-emitter voltage (V_(BE)) of the low-current leakage transistor. Afifth example of the vehicle battery system, optionally including one ormore of the first through fourth examples of the vehicle battery system,further includes wherein the low-current leakage transistor and thecutoff circuit are configured such that a collector-emitter voltage(V_(CE)) of the low-current leakage transistor reduces a voltage acrossthe control input of the cutoff circuit and the output of the cutoffcircuit when the low-current leakage transistor is switched ON. A sixthexample of the vehicle battery system, optionally including one or moreof the first through fifth examples of the vehicle battery system,further includes wherein the WE of the low-current leakage transistor isdecreased to and maintained at less than 1 V when the low-currentleakage transistor is switched ON. A seventh example of the vehiclebattery system, optionally including one or more of the first throughsixth examples of the vehicle battery system, further includes whereinthe BMS comprises a driver integrated circuit, the driver integratedcircuit electrically coupled to the reverse bias protection circuit viathree pins. An eighth example of the vehicle battery system, optionallyincluding one or more of the first through seventh examples of thevehicle battery system, further includes wherein the three pins comprisea first pin configured to switch the cutoff circuit to an ON state, asecond pin configured to switch the cutoff circuit to an OFF state, anda third pin configured as a reference pin for controlling a voltageacross the control input of the cutoff circuit and the output of thecutoff circuit.

In yet another example, a battery management system comprises aprotection circuit comprising a low-current leakage junction transistor,and a MOSFET comprising a drain terminal, a gate terminal, and a sourceterminal, the drain terminal directly coupled to a positive supply lineof a battery pack having a plurality of battery cells, the sourceterminal directly coupled to each of an electrical load and thelow-current leakage junction transistor, and the gate terminal coupledto the low-current leakage junction transistor, wherein the protectioncircuit is configured to maintain the MOSFET in an OFF state in responseto a reverse bias voltage being applied to the source terminal. A firstexample of the battery management system, further includes wherein thelow-current leakage junction transistor comprises a collector terminal,a base terminal, and an emitter terminal, wherein the collector terminalof the low-current leakage junction transistor is coupled to the gateterminal of the MOSFET via each of a first resistor and a first diode,and wherein the emitter terminal of the low-current leakage junctiontransistor is directly coupled to the source terminal of the MOSFET. Asecond example of the battery management system, optionally includingthe first example of the battery management system, further includeswherein the protection circuit comprises a second diode, wherein thesecond diode is a Zener diode, wherein the emitter terminal is furthercoupled to an anode of the second diode, wherein the base terminal iscoupled to a cathode of the second diode via a second resistor, andwherein the second diode is configured to switch the low-current leakagejunction transistor to an ON state by increasing a base-emitter voltage(V_(BE)) of the low-current leakage junction transistor in response tothe reverse bias voltage being applied to the source terminal. A thirdexample of the battery management system, optionally including one ormore of the first and second examples of the battery management system,further includes wherein the first diode is coupled to the collectorterminal to maintain a direction of current flow to the low-currentleakage junction transistor in response to the reverse bias voltagebeing applied to the source terminal. A fourth example of the batterymanagement system, optionally including one or more of the first throughthird examples of the battery management system, further includeswherein decreasing and maintaining the MOSFET in the OFF state comprisesmaintaining a collector-emitter voltage (V_(CE)) of the low-currentleakage junction transistor, the MOSFET maintained in the OFF state bycorrespondingly maintaining a gate-source voltage (V_(GS)) of the MOSFETbelow a threshold voltage (V_(th)) of the MOSFET. A fifth example of thebattery management system, optionally including one or more of the firstthrough fourth examples of the battery management system, furtherincludes wherein decreasing and maintaining the V_(CE) of thelow-current leakage junction transistor comprises decreasing the V_(CE)to and maintaining the V_(CE) at below 1 V. A sixth example of thebattery management system, optionally including one or more of the firstthrough fifth examples of the battery management system, furthercomprises a driver integrated circuit coupled to the protection circuit,wherein the driver integrated circuit is configured to switch the MOSFETto an ON state responsive to receiving a switch ON request generated viaa controller coupled to the driver integrated circuit. A seventh exampleof the battery management system, optionally including one or more ofthe first through sixth examples of the battery management system,further includes wherein the driver integrated circuit comprises a firstoutput, a second output, and a third output, where the first output isconfigured to pull up a voltage of the gate terminal (V_(G)), the secondoutput is configured to pull the V_(G) to ground, and the third outputis configured to regulate a voltage of the source terminal (V_(S)). Aneighth example of the battery management system, optionally includingone or more of the first through seventh examples of the batterymanagement system, further includes wherein two diodes are coupled tothe first output of the driver integrated circuit towards feed a currentto the gate terminal in response to the reverse bias voltage beingapplied to the source terminal. A ninth example of the batterymanagement system, optionally including one or more of the first througheighth examples of the battery management system, further includeswherein a diode is coupled to the second output of the driver integratedcircuit to maintain a direction of current flow to the driver integratedcircuit when the V_(G) is pulled to ground. A tenth example of thebattery management system, optionally including one or more of the firstthrough ninth examples of the battery management system, furtherincludes wherein a diode is coupled to the third output of the driverintegrated circuit to feed a current towards the source terminal inresponse to the reverse bias voltage being applied to the sourceterminal.

In yet another example, a method for managing current flow through abattery pack cutoff circuit comprises flowing a current from a firstnode that is coupled to a control input of the battery pack cutoffcircuit to a second node that is coupled to an output of the batterypack cutoff circuit while preventing current flow across the controlinput to the output in response to a negative voltage being applied tothe second node. A first example of the method further comprises notflowing the current from the first node to the second node in responseto an absence of the negative voltage at the second node. A secondexample of the method, optionally including the first example of themethod, further includes wherein flowing the current from the first nodeto the second node is enabled by activating a transistor. A thirdexample of the method, optionally including one or more of the first andsecond examples of the method, further includes wherein the currentflows from ground to the transistor by flowing through two diodes.

In yet another example, a vehicle battery system comprises a batterymanagement system (BMS) comprising a cutoff circuit electrically coupledto a short-circuit protection circuit, and a battery pack optionallyhaving a plurality of stacked battery cells, where a positive supplyline of the battery pack is electrically coupled to the cutoff circuitand where a ground return line of the battery pack is electricallycoupled to the short-circuit protection circuit, wherein theshort-circuit protection circuit comprises a diode array, where cathodesof the diode array are directly electrically coupled to a positiveterminal post of the battery pack and where anodes of the diode arrayare directly electrically coupled to a negative terminal post of thebattery pack. A first example of the vehicle battery system furtherincludes wherein the cutoff circuit is further electrically coupled to areverse bias protection circuit, where the reverse bias protectioncircuit includes a switchable current path, the switchable current patharranged between a control input of the cutoff circuit and an output ofthe cutoff circuit. A second example of the vehicle battery system,optionally including the first example of the vehicle battery system,further includes wherein the BMS is configured to switch OFF the cutoffcircuit responsive to a short-circuit condition in the vehicle batterysystem, and wherein the BMS is further configured to maintain the cutoffcircuit in an OFF state by flowing an electric current through theswitchable current path and cycling the electric current across thediode array. A third example of the vehicle battery system, optionallyincluding one or more of the first and second examples of the vehiclebattery system, further includes wherein an electrical load iselectrically coupled to the cathodes and the anodes of the diode array,and wherein cycling the electric current across the diode array furtherincludes cycling the electric current across the electrical load. Afourth example of the vehicle battery system, optionally including oneor more of the first through third examples of the vehicle batterysystem, further includes wherein the diode array comprises a pluralityof flyback diodes electrically coupled in parallel. A fifth example ofthe vehicle battery system, optionally including one or more of thefirst through fourth examples of the vehicle battery system, furthercomprises a first busbar electrically coupling the positive supply lineto an input of the cutoff circuit, a second busbar electrically couplingthe positive terminal post to each of an output of the cutoff circuitand the cathodes of the diode array, and a third busbar electricallycoupling the negative terminal post to the anodes of the diode array. Asixth example of the vehicle battery system, optionally including one ormore of the first through fifth examples of the vehicle battery system,further includes wherein the BMS is configured to sequentially flow anelectric current from the first busbar to the second busbar to the thirdbusbar when the cutoff circuit is in an ON state, and wherein the BMS isfurther configured to flow the electric current from the third busbar tothe second busbar when the cutoff circuit is in an OFF state. A seventhexample of the vehicle battery system, optionally including one or moreof the first through sixth examples of the vehicle battery system,further includes wherein the second busbar is configured to reduce afirst parasitic inductance between the diode array and the positiveterminal post, and wherein the third busbar is configured to reduce asecond parasitic inductance between the diode array and the negativeterminal post. An eighth example of the vehicle battery system,optionally including one or more of the first through seventh examplesof the vehicle battery system, further includes wherein the BMS furthercomprises a driver integrated circuit electrically coupled to the cutoffcircuit via three pins. A ninth example of the vehicle battery system,optionally including one or more of the first through eighth examples ofthe vehicle battery system, further includes wherein the three pinscomprise a first pin configured to switch the cutoff circuit to an ONstate, a second pin configured to switch the cutoff circuit to an OFFstate, and a third pin configured as a reference pin for controlling avoltage across a control input of the cutoff circuit and an output ofthe cutoff circuit. A tenth example of the vehicle battery system,optionally including one or more of the first through ninth examples ofthe vehicle battery system, further comprises a shunt resistorelectrically coupling the battery pack to the diode array.

In yet another example, a battery management system comprises aprotection circuit comprising a low-current leakage junction transistorand an array of freewheeling diodes, and a MOSFET comprising a drainterminal, a gate terminal, and a source terminal, where the drainterminal is directly coupled to a positive supply line of a battery packoptionally having a plurality of battery cells, where the sourceterminal is directly coupled to the low-current leakage junctiontransistor, the source terminal further coupled to the array offreewheeling diodes, and where the gate terminal is coupled to thelow-current leakage junction transistor, wherein the protection circuitis configured to, responsive to detection of a voltage greater than avoltage of the battery pack, switch the MOSFET from an ON state to anOFF state and maintain the OFF state. A first example of the batterymanagement system further includes wherein the low-current leakagejunction transistor comprises a collector terminal, a base terminal, andan emitter terminal, wherein the collector terminal of the low-currentleakage junction transistor is coupled to the gate terminal of theMOSFET via a resistor and a diode, and wherein the emitter terminal ofthe low-current leakage junction transistor is directly coupled to thesource terminal of the MOSFET. A second example of the batterymanagement system, optionally including the first example of the batterymanagement system, further includes wherein the diode maintains adirection of current flow to the low-current leakage junction transistorin response to the voltage greater than the voltage of the battery packbeing detected. A third example of the battery management system,optionally including one or more of the first and second examples of thebattery management system, further includes wherein the emitter terminalof the low-current leakage junction transistor is coupled to the arrayof freewheeling diodes via a busbar to maintain a direction of currentflow to the array of freewheeling diodes in response to the voltagegreater than the voltage of the battery pack being detected. A fourthexample of the battery management system, optionally including one ormore of the first through third examples of the battery managementsystem, further comprises a driver integrated circuit coupled to theMOSFET via the protection circuit, wherein the driver integrated circuitis configured to open or close the MOSFET in response to receiving aswitching request generated via a controller coupled to the driverintegrated circuit. A fifth example of the battery management system,optionally including one or more of the first through fourth examples ofthe battery management system, further comprises a current detectioncircuit, the current detection circuit electrically coupled to theMOSFET and communicably coupled to the driver integrated circuit,wherein the current detection circuit is configured to obtain ameasurement of a current flowing to the MOSFET and transmit themeasurement to the controller, the controller configured to detect thevoltage greater than the voltage of the battery pack based on themeasurement.

In yet another example, a method for managing current flow through acutoff circuit of a battery pack, the method comprising flowing acurrent from a first battery terminal to an external load and preventingcurrent flow from a second battery terminal to the first batteryterminal when the cutoff circuit is closed, and flowing the current fromthe second battery terminal to the first battery terminal when thecutoff circuit is open. A first example of the method further comprises,responsive to detecting the current between the battery pack and thecutoff circuit greater than a threshold current, flowing the currentfrom a first node that is coupled to a control input of the cutoffcircuit to a second node that is coupled to an output of the cutoffcircuit while preventing current flow across the control input to theoutput, and responsive to detecting the current between the battery packand the cutoff circuit less than or equal to the threshold current, notflowing the current from the first node to the second node. A secondexample of the method, optionally including the first example of themethod, further comprises, responsive to detecting the current greaterthan the threshold current, opening the cutoff circuit to restrictcurrent flow thereacross.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

1. A battery management system, comprising: a protection circuitcomprising a low-current leakage junction transistor and an array offreewheeling diodes; and a MOSFET comprising a drain terminal, a gateterminal, and a source terminal, where the drain terminal is directlycoupled to a positive supply line of a battery pack, where the sourceterminal is directly coupled to the low-current leakage junctiontransistor, the source terminal further coupled to the array offreewheeling diodes, and where the gate terminal is coupled to thelow-current leakage junction transistor, wherein the protection circuitis configured to, responsive to detection of a voltage greater than avoltage of the battery pack, switch the MOSFET from an ON state to anOFF state and maintain the OFF state.
 2. The battery management systemof claim 1, wherein the low-current leakage junction transistorcomprises a collector terminal, a base terminal, and an emitterterminal, wherein the collector terminal of the low-current leakagejunction transistor is coupled to the gate terminal of the MOSFET via aresistor and a diode, and wherein the emitter terminal of thelow-current leakage junction transistor is directly coupled to thesource terminal of the MOSFET.
 3. The battery management system of claim2, wherein the diode maintains a direction of current flow to thelow-current leakage junction transistor in response to the voltagegreater than the voltage of the battery pack being detected.
 4. Thebattery management system of claim 2, wherein the emitter terminal ofthe low-current leakage junction transistor is coupled to the array offreewheeling diodes via a busbar to maintain a direction of current flowto the array of freewheeling diodes in response to the voltage greaterthan the voltage of the battery pack being detected.
 5. The batterymanagement system of claim 1, further comprising a driver integratedcircuit coupled to the MOSFET via the protection circuit, wherein thedriver integrated circuit is configured to open or close the MOSFET inresponse to receiving a switching request generated via a controllercoupled to the driver integrated circuit.
 6. The battery managementsystem of claim 5, further comprising a current detection circuit, thecurrent detection circuit electrically coupled to the MOSFET andcommunicably coupled to the driver integrated circuit, wherein thecurrent detection circuit is configured to obtain a measurement of acurrent flowing to the MOSFET and transmit the measurement to thecontroller, the controller configured to detect the voltage greater thanthe voltage of the battery pack based on the measurement.
 7. A batterymanagement system, comprising: a protection circuit comprising alow-current leakage junction transistor, an array of freewheelingdiodes; a MOSFET comprising a drain terminal, a gate terminal, and asource terminal; a driver integrated circuit coupled to the MOSFET viathe protection circuit; and a current detection circuit communicablycoupled to the driver integrated circuit, wherein the protection circuitis configured to, responsive to detection of a voltage greater than avoltage of a battery pack, switch the MOSFET from an ON state to an OFFstate and maintain the OFF state.
 8. The battery management system ofclaim 7, wherein the drain terminal of the MOSFET is directly coupled toa positive supply line of the battery pack, and wherein the sourceterminal of the MOSFET is directly coupled to the low-current leakagejunction transistor, the source terminal further coupled to the array offreewheeling diodes, and wherein the gate terminal is coupled to thelow-current leakage junction transistor.
 9. The battery managementsystem of claim 7, wherein the driver integrated circuit is configuredto open or close the MOSFET in response to receiving a switching requestgenerated via a controller coupled to the driver integrated circuit. 10.The battery management system of claim 7, wherein the current detectioncircuit electrically coupled to the MOSFET.
 11. The battery managementsystem of claim 10, wherein current detection circuit is configured toobtain a measurement of a current flowing to the MOSFET and transmit themeasurement to a controller, the controller configured to detect thevoltage greater than the voltage of the battery pack based on themeasurement.
 12. The battery management system of claim 7, wherein thelow-current leakage junction transistor comprises a collector terminal,a base terminal, and an emitter terminal, wherein the collector terminalof the low-current leakage junction transistor is coupled to the gateterminal of the MOSFET via a resistor and a diode, and wherein theemitter terminal of the low-current leakage junction transistor isdirectly coupled to the source terminal of the MOSFET.
 13. The batterymanagement system of claim 12, wherein the diode maintains a directionof current flow to the low-current leakage junction transistor inresponse to the voltage greater than the voltage of the battery packbeing detected.
 14. A battery management system, comprising: aprotection circuit comprising a low-current leakage junction transistor,and array of freewheeling diodes; a MOSFET comprising a drain terminal,a gate terminal, and a source terminal, wherein the low-current leakagejunction transistor comprises a collector terminal, a base terminal, andan emitter terminal; and wherein the emitter terminal of the low-currentleakage junction transistor is coupled to the array of freewheelingdiodes via a busbar to maintain a direction of current flow to the arrayof freewheeling diodes in response to the voltage greater than thevoltage of a battery pack being detected.
 15. The battery managementsystem of claim 14, wherein the drain terminal of the MOSFET is directlycoupled to a positive supply line of the battery pack, and wherein thesource terminal of the MOSFET is directly coupled to the low-currentleakage junction transistor, the source terminal further coupled to thearray of freewheeling diodes, and wherein the gate terminal is coupledto the low-current leakage junction transistor.
 16. The batterymanagement system of claim 14, wherein the collector terminal of thelow-current leakage junction transistor is coupled to the gate terminalof the MOSFET via a resistor and a diode, and wherein the emitterterminal of the low-current leakage junction transistor is directlycoupled to the source terminal of the MOSFET.
 17. The battery managementsystem of claim 16, wherein the diode maintains a direction of currentflow to the low-current leakage junction transistor in response to thevoltage greater than the voltage of the battery pack being detected. 18.The battery management system of claim 14, further comprising a driverintegrated circuit coupled to the MOSFET via the protection circuit,wherein the driver integrated circuit is configured to open or close theMOSFET in response to receiving a switching request generated via acontroller coupled to the driver integrated circuit.
 19. The batterymanagement system of claim 18, further comprising a current detectioncircuit, the current detection circuit electrically coupled to theMOSFET and communicably coupled to the driver integrated circuit. 20.The battery management system of claim 19, wherein the current detectioncircuit is configured to obtain a measurement of a current flowing tothe MOSFET and transmit the measurement to the controller, thecontroller configured to detect the voltage greater than the voltage ofthe battery pack based on the measurement.